Field devices of automation- and/or process measurements technology are applied, for example, in industrial plants and serve there for ascertaining and/or monitoring and/or for displaying a process variable, such as, for example, flow, fill level, pressure, temperature or pH-value of a measured substance or material. These field devices are often connected communicatively among one another and/or with a superordinated unit.
For data transmission between the field devices and/or the superordinated unit, a series of fieldbus systems are known from the state of the art. Currently used for data transmission via the fieldbus systems are standardized protocols, such as, for example, the HART, Profibus or Foundation Fieldbus protocols as well as also different Ethernet standards. The communicative connection between the field devices and/or the superordinated unit is referred to in the following as the communication channel. The communication channel can, on the other hand, such as described in an example of an embodiment of the present invention, be formed of a transmission path for transmission of the frequency-modulated signal between the transmitting unit and the receiving unit of the proposed apparatus, in the case of which such is preferably a field device.
Known from German Patent DE 102007062919 A1 for diagnosis of operating- and environmental conditions of such field devices is an apparatus, which has a control/evaluation unit, which ascertains a present loop current. To this end, a measuring resistor is integrated in the field device.
Furthermore, known from German Patent DE 102009050645 A1 is a field device, in the case of which, for monitoring an analog output signal produced by the field devices, a first read-back channel is present for the analog output signal. The analog output signal is compared with a comparison signal for ascertaining a deviation.
These evaluating- and diagnostic apparatuses known from the state of the art refer, however, all to an analog output signal, or to the information transmitted by means of the communication signal. A (purely) physical evaluation of the fieldbus protocols known from the state of the art can, however, not be achieved in this way. Especially, it is not known from the state of the art to ascertain, based on the (digital) communication signal (per se), the quality of the signal transmission via the fieldbus.